Chemoresistance poses one of the most significant challenges of cancer therapy. Carboplatin (CbPt) is one of the most used chemotherapeutics in ovarian cancer (OVC) treatment. MRE11 constitutes a part of homologous recombination (HR), which is responsible for the repair of CbPt-induced DNA damage, particularly DNA crosslinks. The study's main aim was to address the role of HR in CbPt chemoresistance in OVC and to evaluate the possibility of overcoming CbPt chemoresistance by Mirin-mediated MRE11 inhibition in an OVC cell line. Lower expression of MRE11 was associated with better overall survival in a cohort of OVC patients treated with platinum drugs (TCGA dataset, P < 0.05). Using in vitro analyses, we showed that the high expression of HR genes drives the CbPt chemoresistance in our CbPt-resistant cell line model. Moreover, the HR inhibition by Mirin not only increased sensitivity to carboplatin (P < 0.05) but also rescued the sensitivity in the CbPt-resistant model (P < 0.05). Our results suggest that MRE11 inhibition with Mirin may represent a promising way to overcome OVC resistance. More therapy options will ultimately lead to better personalized cancer therapy and improvement of patients' survival.

• MeSH
• Drug Resistance, Neoplasm * genetics   drug effects   MeSH
• MRE11 Homologue Protein * genetics   MeSH
• Carboplatin * pharmacology   therapeutic use   MeSH
• Humans MeSH
• Cell Line, Tumor MeSH
• Ovarian Neoplasms * drug therapy   genetics   MeSH
• DNA Damage drug effects   MeSH
• Antineoplastic Agents pharmacology   therapeutic use   MeSH
• Gene Expression Regulation, Neoplastic drug effects   MeSH
• Recombinational DNA Repair * drug effects   MeSH
• Check Tag
• Humans MeSH
• Female MeSH
• Publication type
• Journal Article MeSH

MRE11 nuclease is a central player in signaling and processing DNA damage, and in resolving stalled replication forks. Here, we describe the identification and characterization of new MRE11 inhibitors MU147 and MU1409. Both compounds inhibit MRE11 nuclease more specifically and effectively than the relatively weak state-of-the-art inhibitor mirin. They also abrogate double-strand break repair mechanisms that rely on MRE11 nuclease activity, without impairing ATM activation. Inhibition of MRE11 also impairs nascent strand degradation of stalled replication forks and selectively affects BRCA2-deficient cells. Herein, we illustrate that our newly discovered compounds MU147 and MU1409 can be used as chemical probes to further explore the biological role of MRE11 and support the potential clinical relevance of pharmacological inhibition of this nuclease.

• MeSH
• MRE11 Homologue Protein * metabolism   antagonists & inhibitors   MeSH
• Enzyme Inhibitors * pharmacology   chemistry   chemical synthesis   MeSH
• Humans MeSH
• Molecular Structure MeSH
• Drug Discovery MeSH
• DNA Repair drug effects   MeSH
• Dose-Response Relationship, Drug MeSH
• Structure-Activity Relationship MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH

The MRE11, RAD50, and NBN genes encode the MRN complex sensing DNA breaks and directing their repair. While carriers of biallelic germline pathogenic variants (gPV) develop rare chromosomal instability syndromes, the cancer risk in heterozygotes remains controversial. We performed a systematic review and meta-analysis of 53 studies in patients with different cancer diagnoses to better understand the cancer risk. We found an increased risk (odds ratio, 95% confidence interval) for gPV carriers in NBN for melanoma (7.14; 3.30-15.43), pancreatic cancer (4.03; 2.14-7.58), hematological tumors (3.42; 1.14-10.22), and prostate cancer (2.44, 1.84-3.24), but a low risk for breast cancer (1.29; 1.00-1.66) and an insignificant risk for ovarian cancer (1.53; 0.76-3.09). We found no increased breast cancer risk in carriers of gPV in RAD50 (0.93; 0.74-1.16; except of c.687del carriers) and MRE11 (0.87; 0.66-1.13). The secondary burden analysis compared the frequencies of gPV in MRN genes in patients from 150 studies with those in the gnomAD database. In NBN gPV carriers, this analysis additionally showed a high risk for brain tumors (5.06; 2.39-9.52), a low risk for colorectal (1.64; 1.26-2.10) and hepatobiliary (2.16; 1.02-4.06) cancers, and no risk for endometrial, and gastric cancer. The secondary burden analysis showed also a moderate risk for ovarian cancer (3.00; 1.27-6.08) in MRE11 gPV carriers, and no risk for ovarian and hepatobiliary cancers in RAD50 gPV carriers. These findings provide a robust clinical evidence of cancer risks to guide personalized clinical management in heterozygous carriers of gPV in the MRE11, RAD50, and NBN genes.

• MeSH
• DNA-Binding Proteins genetics   MeSH
• DNA Repair Enzymes genetics   MeSH
• Genetic Predisposition to Disease * MeSH
• MRE11 Homologue Protein * genetics   MeSH
• Acid Anhydride Hydrolases * genetics   MeSH
• Nuclear Proteins * genetics   MeSH
• Humans MeSH
• Neoplasms * genetics   MeSH
• Cell Cycle Proteins * genetics   MeSH
• Germ-Line Mutation * MeSH
• Check Tag
• Humans MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Meta-Analysis MeSH
• Systematic Review MeSH

DNA double-strand breaks (DSBs), such as those produced by radiation and radiomimetics, are amongst the most toxic forms of cellular damage, in part because they involve extensive oxidative modifications at the break termini. Prior to completion of DSB repair, the chemically modified termini must be removed. Various DNA processing enzymes have been implicated in the processing of these dirty ends, but molecular knowledge of this process is limited. Here, we demonstrate a role for the metallo-β-lactamase fold 5'-3' exonuclease SNM1A in this vital process. Cells disrupted for SNM1A manifest increased sensitivity to radiation and radiomimetic agents and show defects in DSB damage repair. SNM1A is recruited and is retained at the sites of DSB damage via the concerted action of its three highly conserved PBZ, PIP box and UBZ interaction domains, which mediate interactions with poly-ADP-ribose chains, PCNA and the ubiquitinated form of PCNA, respectively. SNM1A can resect DNA containing oxidative lesions induced by radiation damage at break termini. The combined results reveal a crucial role for SNM1A to digest chemically modified DNA during the repair of DSBs and imply that the catalytic domain of SNM1A is an attractive target for potentiation of radiotherapy.

• MeSH
• DNA metabolism   genetics   MeSH
• DNA Breaks, Double-Stranded * radiation effects   MeSH
• DNA Repair Enzymes * metabolism   genetics   MeSH
• Exodeoxyribonucleases * metabolism   genetics   MeSH
• Humans MeSH
• DNA Repair * MeSH
• Proliferating Cell Nuclear Antigen metabolism   genetics   MeSH
• Cell Cycle Proteins MeSH
• Ubiquitination MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH

Meiotic recombination is of central importance for the proper segregation of homologous chromosomes, but also for creating genetic diversity. It is initiated by the formation of double-strand breaks (DSBs) in DNA catalysed by evolutionarily conserved Spo11, together with additional protein partners. Difficulties in purifying the Spo11 protein have limited the characterization of its biochemical properties and of its interactions with other DSB proteins. In this study, we have purified fragments of Spo11 and show for the first time that Spo11 can physically interact with Mre11 and modulates its DNA binding, bridging, and nuclease activities. The interaction of Mre11 with Spo11 requires its far C-terminal region, which is in line with the severe meiotic phenotypes of various mre11 mutations located at the C-terminus. Moreover, calibrated ChIP for Mre11 shows that Spo11 promotes Mre11 recruitment to chromatin, independent of DSB formation. A mutant deficient in Spo11 interaction severely reduces the association of Mre11 with meiotic chromatin. Consistent with the reduction of Mre11 foci in this mutant, it strongly impedes DSB formation, leading to spore death. Our data provide evidence that physical interaction between Spo11 and Mre11, together with end-bridging, promote normal recruitment of Mre11 to hotspots and DSB formation.

• MeSH
• Chromatin * metabolism   MeSH
• DNA-Binding Proteins metabolism   genetics   MeSH
• DNA Breaks, Double-Stranded * MeSH
• Endodeoxyribonucleases * metabolism   genetics   MeSH
• Exodeoxyribonucleases metabolism   genetics   MeSH
• Meiosis * genetics   MeSH
• Mutation MeSH
• Saccharomyces cerevisiae Proteins * metabolism   genetics   MeSH
• Saccharomyces cerevisiae cytology   genetics   metabolism   MeSH
• Protein Binding MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Targeting poly(ADP-ribose) glycohydrolase (PARG) is currently explored as a therapeutic approach to treat various cancer types, but we have a poor understanding of the specific genetic vulnerabilities that would make cancer cells susceptible to such a tailored therapy. Moreover, the identification of such vulnerabilities is of interest for targeting BRCA2;p53-deficient tumors that have acquired resistance to poly(ADP-ribose) polymerase inhibitors (PARPi) through loss of PARG expression. Here, by performing whole-genome CRISPR/Cas9 drop-out screens, we identify various genes involved in DNA repair to be essential for the survival of PARG;BRCA2;p53-deficient cells. In particular, our findings reveal EXO1 and FEN1 as major synthetic lethal interactors of PARG loss. We provide evidence for compromised replication fork progression, DNA single-strand break repair, and Okazaki fragment processing in PARG;BRCA2;p53-deficient cells, alterations that exacerbate the effects of EXO1/FEN1 inhibition and become lethal in this context. Since this sensitivity is dependent on BRCA2 defects, we propose to target EXO1/FEN1 in PARPi-resistant tumors that have lost PARG activity. Moreover, EXO1/FEN1 targeting may be a useful strategy for enhancing the effect of PARG inhibitors in homologous recombination-deficient tumors.

• MeSH
• Flap Endonucleases genetics   metabolism   therapeutic use   MeSH
• DNA Repair Enzymes genetics   MeSH
• Exodeoxyribonucleases genetics   MeSH
• Glycoside Hydrolases genetics   metabolism   MeSH
• Humans MeSH
• Tumor Suppressor Protein p53 * genetics   metabolism   MeSH
• Neoplasms * drug therapy   genetics   MeSH
• DNA Repair MeSH
• Poly(ADP-ribose) Polymerase Inhibitors pharmacology   MeSH
• DNA Damage MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH

The MRE11, RAD50, and NBN genes encode for the nuclear MRN protein complex, which senses the DNA double strand breaks and initiates the DNA repair. The MRN complex also participates in the activation of ATM kinase, which coordinates DNA repair with the p53-dependent cell cycle checkpoint arrest. Carriers of homozygous germline pathogenic variants in the MRN complex genes or compound heterozygotes develop phenotypically distinct rare autosomal recessive syndromes characterized by chromosomal instability and neurological symptoms. Heterozygous germline alterations in the MRN complex genes have been associated with a poorly-specified predisposition to various cancer types. Somatic alterations in the MRN complex genes may represent valuable predictive and prognostic biomarkers in cancer patients. MRN complex genes have been targeted in several next-generation sequencing panels for cancer and neurological disorders, but interpretation of the identified alterations is challenging due to the complexity of MRN complex function in the DNA damage response. In this review, we outline the structural characteristics of the MRE11, RAD50 and NBN proteins, the assembly and functions of the MRN complex from the perspective of clinical interpretation of germline and somatic alterations in the MRE11, RAD50 and NBN genes.

• MeSH
• Ataxia Telangiectasia Mutated Proteins genetics   metabolism   MeSH
• DNA-Binding Proteins genetics   metabolism   MeSH
• DNA Repair Enzymes genetics   metabolism   MeSH
• MRE11 Homologue Protein genetics   metabolism   MeSH
• Acid Anhydride Hydrolases genetics   metabolism   MeSH
• Nuclear Proteins genetics   metabolism   MeSH
• Humans MeSH
• Tumor Suppressor Proteins * genetics   MeSH
• DNA Repair genetics   MeSH
• Cell Cycle Proteins * metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Review MeSH

A growing body of evidence supports the notion that cancer resistance is driven by a small subset of cancer stem cells (CSC), responsible for tumor initiation, growth, and metastasis. Both CSC and chemoresistant cancer cells may share common qualities to activate a series of self-defense mechanisms against chemotherapeutic drugs. Here, we aimed to identify proteins in chemoresistant triple-negative breast cancer (TNBC) cells and corresponding CSC-like spheroid cells that may contribute to their resistance. We have identified several candidate proteins representing the subfamilies of DNA damage response (DDR) system, the ATP-binding cassette, and the 26S proteasome degradation machinery. We have also demonstrated that both cell types exhibit enhanced DDR when compared to corresponding parental counterparts, and identified RAD50 as one of the major contributors in the resistance phenotype. Finally, we have provided evidence that depleting or blocking RAD50 within the Mre11-Rad50-NBS1 (MRN) complex resensitizes CSC and chemoresistant TNBC cells to chemotherapeutic drugs.

• MeSH
• Drug Resistance, Neoplasm drug effects   genetics   MeSH
• Cisplatin administration & dosage   MeSH
• Cyclophosphamide administration & dosage   MeSH
• DNA-Binding Proteins genetics   MeSH
• Doxorubicin administration & dosage   MeSH
• DNA Repair Enzymes genetics   MeSH
• MRE11 Homologue Protein genetics   MeSH
• Acid Anhydride Hydrolases genetics   MeSH
• Nuclear Proteins genetics   MeSH
• Humans MeSH
• Neoplastic Stem Cells drug effects   metabolism   MeSH
• DNA Damage drug effects   MeSH
• Disease-Free Survival MeSH
• Cell Cycle Proteins genetics   MeSH
• Triple Negative Breast Neoplasms drug therapy   genetics   MeSH
• Check Tag
• Humans MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Nonspecific structural chromosomal aberrations (CAs) can be found at around 1% of circulating lymphocytes from healthy individuals but the frequency may be higher after exposure to carcinogenic chemicals or radiation. The frequency of CAs has been measured in occupational monitoring and an increased frequency of CAs has also been associated with cancer risk. Alterations in DNA damage repair and telomere maintenance are thought to contribute to the formation of CAs, which include chromosome type of aberrations and chromatid type of aberrations. In the present study, we used the result of our published genome-wide association studies to extract data on 153 DNA repair genes from 866 nonsmoking persons who had no known occupational exposure to genotoxic substances. Considering an arbitrary cut-off level of P< 5 × 10-3, single nucleotide polymorphisms (SNPs) tagging 22 DNA repair genes were significantly associated with CAs and they remained significant at P < 0.05 when adjustment for multiple comparisons was done by the Binomial Sequential Goodness of Fit test. Nucleotide excision repair pathway genes showed most associations with 6 genes. Among the associated genes were several in which mutations manifest CA phenotype, including Fanconi anemia, WRN, BLM and genes that are important in maintaining genome stability, as well as PARP2 and mismatch repair genes. RPA2 and RPA3 may participate in telomere maintenance through the synthesis of the C strand of telomeres. Errors in NHEJ1 function may lead to translocations. The present results show associations with some genes with known CA phenotype and suggest other pathways with mechanistic rationale for the formation of CAs in healthy nonsmoking population.

• MeSH
• White People genetics   MeSH
• Genome-Wide Association Study MeSH
• Chromosome Aberrations * MeSH
• DNA-Binding Proteins genetics   MeSH
• Adult MeSH
• DNA Repair Enzymes genetics   MeSH
• RecQ Helicases genetics   MeSH
• Werner Syndrome Helicase genetics   MeSH
• Polymorphism, Single Nucleotide * MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Non-Smokers * MeSH
• DNA Mismatch Repair genetics   MeSH
• DNA Repair genetics   MeSH
• Computer Simulation MeSH
• Poly(ADP-ribose) Polymerases genetics   MeSH
• Replication Protein A genetics   MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Healthy Volunteers MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Male MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Multicenter Study MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Czech Republic MeSH
• Slovakia MeSH

DNA damage tolerance (DDT) and homologous recombination (HR) stabilize replication forks (RFs). RAD18/UBC13/three prime repair exonuclease 2 (TREX2)-mediated proliferating cell nuclear antigen (PCNA) ubiquitination is central to DDT, an error-prone lesion bypass pathway. RAD51 is the recombinase for HR. The RAD51 K133A mutation increased spontaneous mutations and stress-induced RF stalls and nascent strand degradation. Here, we report in RAD51K133A cells that this phenotype is reduced by expressing a TREX2 H188A mutation that deletes its exonuclease activity. In RAD51K133A cells, knocking out RAD18 or overexpressing PCNA reduces spontaneous mutations, while expressing ubiquitination-incompetent PCNAK164R increases mutations, indicating DDT as causal. Deleting TREX2 in cells deficient for the RF maintenance proteins poly(ADP-ribose) polymerase 1 (PARP1) or FANCB increased nascent strand degradation that was rescued by TREX2H188A, implying that TREX2 prohibits degradation independent of catalytic activity. A possible explanation for this occurrence is that TREX2H188A associates with UBC13 and ubiquitinates PCNA, suggesting a dual role for TREX2 in RF maintenance.

• MeSH
• Exodeoxyribonucleases genetics   metabolism   MeSH
• Phosphoproteins genetics   metabolism   MeSH
• Humans MeSH
• Mutation * MeSH
• Mice MeSH
• Rad51 Recombinase biosynthesis   genetics   metabolism   MeSH
• DNA Replication * MeSH
• Transfection MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH